This invention relates to a process of forming a metal or metal compound coating on a face of a heated glass substrate during its displacement in a given direction by contacting such face at a coating station through which the substrate passes, with at least one stream of droplets comprising a substance or substances from which said coating metal or metal compound is formed on said face. The invention also relates to apparatus for use in carrying out such a process.
Such a process can be employed for coating glass sheets and for coating a continuous freshly formed ribbon of flat glass. The process can be used for forming coatings, e.g. metal oxide coatings, which modify the apparent colour of the glass and/or which have some other required properties in respect of incident radiation, e.g. an infra-red-reflecting property.
Problems are encountered in forming coatings which have uniform properties. This is partly due to the difficulty of ensuring uniformity of the structure and thickness of the coating from one zone to another.
Various proposals have been made for promoting the formation of uniform coatings, including the discharge of the coating material as a stream which is inclined downwardly towards the substrate in the direction of its conveyance, and the creation of suction forces in exhaust ducting situated so as to cause gases environmental to the droplet stream to flow away from such stream and into such ducting (cf. United Kingdom Pat. Nos. 1 516 032 and 1 523 991).
Even when observing conditions hitherto proposed in this art, defects sometimes occur within or at the surface of the coating. These defects although often not prominent, nevertheless disqualify the product from the top quality ratings which are now in demand. If the defects are at the surface of the coating, the quality of the product can in some but not all cases be improved by an after-coating surfacing treatment, but of course such additional treatments add to the product costs.